1. Field of the Invention
The present invention relates to a method and a device for sealing a doubled web while pressing the side thereof, and in particular relates to a packaging container producing method and equipment by which a plate-like web is molded to a tubular web, and contents such as fluid food, etc. are filled in the tubular web.
2. Description of the Related Art
Plate-like web wound like a roll is moved while being continuously unwound, in order to gradually mold it to be tubular, the web is continuously adhered to each other at the position where both ends thereof in the direction orthogonal to the lengthwise direction of the web slightly overlap, and a filling liquid such as a fluid food is filled therein. In order to continuously form packaging containers in which the filling liquid is fully filled, the packaging containers are enclosed below the level of the filling liquid and is sealed (cross sealed) in the direction orthogonal to the web lengthwise direction. Thereafter, nearly the central portion of the abovementioned cross-sealed part in its width direction is cut off. That is, by repeating a series of these operations, a liquid filling packaging container is formed, wherein finally, a parallel-hexahedral container is produced.
When filling a filling liquid such as fluid food into a web, two pairs of sealing jaws are provided, which cross seal a web in such a state that the web is pressed from both sides thereof, and the tubular web being transferred downward is put and nipped between the respective pairs of sealing jaws which move along with the web while pulling the web. After the sealing jaws shift down an appointed distance, nearly the central portion of the cross-sealing part is cut off as described above, and simultaneously the web sealing state is opened to cancel the downward transfer force of the tubular web, wherein the sealing jaws are caused to move in a direction of being spaced from each other, and elevated an appointed distance, and the process of sealing the tubular web is repeated.
Tubular web is composed of a multi-layered structure consisting of a polyethylene film layer, adhesive glue layer, aluminum foil layer, paper layer, and polyethylene film layer from the inside in that order. The cross sealing of the tubular web is carried out by heating and melting the polyethylene film layer using the abovementioned pair of sealing jaws.
A pair of sealing jaws consists of, for example, as shown in FIG. 2 and FIG. 3, a heat sealing jaw 7a for heat-sealing, and a pressure receiving jaw 7b to receive a compression force from the heat sealing jaw 7a (although, in FIG. 2, there is a pair of heat sealing jaw 7a and a pressure receiving jaw 7b, and there is a pair of a heat sealing jaw 7a' and a pressure receiving jaw 7b', hereinafter the description deals with only the pair of heat sealing jaw 7a and pressure receiving jaw 7b), an inductor 8 is provided at the contacting portion of the heat sealing jaw 7a with the web surface, and a pressure receiving bar 9 and a cutter 11, which cuts off the middle portion of the cross-sealed part in the width direction, are secured at the contacting portion of the pressure receiving jaw 7b with the web W. Furthermore, a hook 16a and a hook 16b are provided at both ends of the heat sealing jaw 7a and pressure receiving jaw 7b, respectively, wherein the hook 16a of the heat sealing jaw 7a is engaged with the hook 16b of the pressure receiving jaw 7b, and the engaging force in the cross sealing of web W nipped between the inductor 8 and pressure receiving bar 9 is controlled by adjusting the working oil pressure of a liquid pressure cylinder 18 of the hook 16a.
Subsequently, an eddy current is caused to flow to the aluminum foil of web W by the inductor 8 of the heat seal jaw 7a when both sides of the web are pressed by the heat seal jaw 7a and pressure receiving jaw 7b of a pair of seal jaws 7, wherein heat is generated by induction heating. With this heat, the polyethylene film layer is melted to cause the web W to be cross-sealed.
The cross sealing of web W is carried out by the following six processes as shown in FIG. 7.
(1) Exclusion of the filled liquid below the level in the web PA1 (2) Heating at an appointed output for an appointed duration of time from the outside of web PA1 (3) Cooling of the web PA1 (4) Cutting at the cross-sealed portion (Separation of pillow-like containers) PA1 (5) Holding of the web PA1 (6) Pressing at an appointed level of pressure for an appointed duration of time
Although the web is cross-sealed by the abovementioned six processes, as shown in FIG. 7, the pressing process in (6) is carried out to press the web throughout processes (1) through (5).
As shown in FIG. 8, exclusion of the filled liquid in the web at the abovementioned cross-sealing portion is a process for excluding the filled liquid remaining in the cross-sealing portion inside the web W when the heat seal jaw 7a and pressure receiving jaw 7b press both sides of web W.
Conventionally, the web pressing force for cross-sealing in the respective cycles (1) through (6) at the cross sealing process has been controlled while visibly checking the working oil pressure generator of liquid pressure cylinder 18 for adjusting the engaging force of hooks 16a and 16b with an analog type gauge. Therefore, the pressing force has not been controlled while checking the sealing pressure directly influenced on the web W.
In most cases, one cycle (1) through (6) is carried out in a very short time 1 second or less per hexahedral packaging container which is the final product.
However, in the abovementioned process of cross sealing below the liquid level, which is carried out in a very short time 1 second or less per packaging container, it was impossible to detect, in real time, whether or not the operation is reliably carried out every time.